A group of sensory scientists who have cooperated formally and informally for many years proposes to focus their joint research on specific, long-range problems of intensity effects and processing in the auditory and tactile systems. A multidisciplinary approach will be used, including 1) human and animal behavior, 2) neurophysiology, and 3) neuroanatomy, with the specific goal of providing definitive answers to still unresolved problems of transduction and intensity coding in the two sensory systems. Specific experiments within the sensory modalities will run partially parallel and partially complementary courses, so that the three component projects are interlocked in their goals. The approach of systems analysis will be used. Global functions will be determined from human psychophysics and animal behavior (Component Project-1). Project-1 experiments are focused on the relation between intensity discrimination and loudness, intensity effects in the discrimination of complex stimuli, and the correlation of behavioral and neural responses. The contributions of relevant components of the systems to the global functions will be sought through direct physiological (Component Project-2) and morphological (Component Project-3) experiments aided by mathematical analysis. Project-2 experiments concern the effects of stimulus intensity on the magnitude and variability of neural responses in the cochlea, auditory nerve, and cochlear nucleus. Project-3 is targeted on the role in transduction and intensity effects played by the auditory hair-cell coat and stereociliar arrangement, and by the cytoplasmic extensions of the Pacinian-corpuscle axon. The experiments will involve vertebrate animals, including humans. All of the proposed experiments are consistent with our group's expertise and long- range goals of elucidating questions of fundamental importance to our understanding of the neural mechanisms underlying human behavior.